Licorice is known as a crude drug, and a primary component of its water extract, i.e., glycyrrhizin (glycyrrhizinic acid), has excellent pharmacodynamic actions, such as anti-inflammatory action, antitumor action, and antiallergic action. Thus, it has been extensively used for food, medical supplies, cosmetics, and other applications. Since the glycyrrhizin is approximately 200 times sweeter than sucrose, it has been used as a sweetener.
Hydrophobic components of the licorice, which are extracted from the licorice or a residue of a licorice water extract with an organic solvent or the like, exhibit many useful actions, such as antioxidant action, antibacterial action, enzyme inhibitory action, antitumor action, antiallergic action, or antiviral action. Such hydrophobic components of the licorice, however, are not substantially dissolved in water or common oil, and are likely to be solidified and colored in the state of an organic solvent extract. Due to such unstable properties, use of such components is difficult.
Such difficulty has been overcome by, for example, a method wherein a fat solvent comprising an oil-soluble fatty acid ester of a polyhydric alcohol in an amount of at least 10% thereof is mixed with a hydrophobic licorice extract (WO 03/084556). However, it has been difficult to dissolve such fat composition comprising hydrophobic components of the licorice in an aqueous substance.
JP Patent Publication (kokai) No. 2-204417 (1990) discloses the preparation of an oil-in-water emulsion composition from a solution of a hydrophobic licorice flavonoid in medium-chain fatty acid triglyceride in the presence of an emulsifying agent. This invention, however, is intended to realize water dispersibility and not transparency or acid resistance.
JP Patent Publication (kokai) No. 2003-176233 proposes a composition comprising a licorice oil extract and polyglycerin lauric acid ester.
WO 2005/011672 discloses concentrated milk involving the use of a fat composition comprising hydrophobic components of licorice and fatty acid ester of glycerin as an emulsifying agent. This concentrated milk, however, is a non-transparent emulsified product and thus is not considered to be adequate for applications that require transparency.
Furthermore, EP 1249230 discloses that an administration of an oil-soluble substance to the body in a microemulsion preconcentrate form enhances the rate of systemic absorption. In this technique, the microemulsion preconcentrate means a solution of a lipophilic substance in an emulsifying agent, which forms a microemulsion. The microemulsion preconcentrate is an auto-emulsified preparation that forms submicron-order microemulsions upon contact with an aqueous medium.